Recently, most switching power supply apparatuses are controlled in a digital manner, so that the complicated algorithm can be realized more easily, and more kinds of electronic products can be realized. In addition, the digital control mechanism can provide more flexible control interface to the digital power devices.
As known, a multi-stage power converter has a complicated circuit structure. If the multi-stage power converter is controlled in the digital manner, many benefits can be achieved. Conventionally, the multi-stage power converter comprises plural power conversion circuits, and the plural power conversion circuits are isolated through a transformer. Moreover, each power conversion circuit is controlled according to a closed-loop control mechanism. Consequently, the location of the control unit becomes an important issue.
Conventionally, there are many approaches to locate the control units. In accordance with one approach, each stage of the multi-stage power converter comprises an individual control unit to perform the closed-loop control operation of each stage. In accordance with another approach, a main control unit is used for performing the closed-loop control operations of all stages. Moreover, the feedback signals from different isolated sides of the main control unit are transmitted to the main control unit through a conventional communication method. In accordance with a third approach, a main control unit is used for performing the closed-loop control operations of all stages. In addition, the feedback signals from different isolated sides of the main control unit are transmitted to the main control unit through a linear optocoupler.
However, the above approaches have some drawbacks. For example, the first approach increases the circuit complexity. Moreover, the uses of plural control units increase the debugging complexity. The second approach uses the conventional communication method (e.g., I2C, CAN or SPI) to transmit the feedback signals to the main control unit. Consequently, the balance between the communication speed and the hardware resource should be taken into consideration. However, information is transmission in a form of a frame. Each frame contains a lot of meaningless information for the control operation. For effectively transmitting information at a desired speed, the working speed of the hardware components should be largely increased. That is, the main control unit used in the multi-stage power converter needs to have enhanced computing capability. Since the main control unit is costly, the fabricating cost of the multi-stage power converter is increased. The third approach uses the linear optocoupler to transmit the feedback signals to the main control unit. However, the linear optocoupler has many problems such as a temperature drift effect and an aging problem. Under this circumstance, the operations of the multi-stage power converter are possibly abnormal.
Therefore, there is a need of providing an improved multi-stage power converter and a control method of the multi-stage power converter in order to overcome the above drawbacks.